Generally, the polyolefin is characterized by being superior in moldability, heat resistance, mechanical properties, chemical resistance, hygiene suitability and water-resistant steam permeability and excellent in the outward appearance of its molded articles, and is thus used widely in extrusion-molded articles, hollow molded articles, and injection-molded articles.
However, the polyolefin generally does not contain a polar group in its molecule and is thus poor in compatibility with polar resin such as nylon and EVOH and in adhesion to polar resin and metal, to make it hardly utilizable as a blend or a laminate with such materials.
To solve these problems, a method of improving the affinity of the polyolefin for polar resin by grafting a polar group-containing monomer onto the polyolefin has been widely carried out. In this method, however, the polyolefin undergoes intermolecular crosslinkage or molecular-chain cleavage together with the graft reaction, and therefore the resulting graft polymer hardly matches with the viscosity of polar resin or is poor in compatibility therewith in some cases. Further, a gelled material formed through intermolecular crosslinkage or molecular-chain cleavage can deteriorate the outward appearance of its molded articles.
JP-A 2-51511 and JP-A 3-177403 describe a method of copolymerizing α-olefin with a polar group-containing monomer by using a titanium- or vanadium-based catalyst. According to this method, the intermolecular crosslinkage and molecular-chain cleavage described above hardly occur, but the molecular structure of the resulting copolymer is heterogeneous, that is, the molecular-weight distribution is broad, or the inversion content is high, and thus the orientation of polar groups in an interface between themselves and a polar substance is not sufficient, resulting sometimes in insufficient adhesion to and compatibility with the polar substance.
JP-A2002-145947 and JP-A2002-155109 filed by the present applicant disclose a new branched polar group-containing olefin copolymer, a process for producing the same, a thermoplastic resin composition comprising the same, and uses thereof, to solve a majority of the problems. According to the disclosure, a branched moiety of the branched polar group-containing olefin copolymer is prepared and added by any chain extension reaction such as anion polymerization, ring-opening polymerization and polycondensation.
However, there is the problem of a limitation to starting monomers usable in the chain extension reaction. Particularly, the polycondensation reaction is not only subject to a severe limit to usable starting monomers, but is also subject to severe reaction conditions in general, thus sometimes causing deterioration in the polymer. From this viewpoint, there is demand for further improved branched olefin copolymers.
T. C. Chung et al. reported, in U.S. Pat. No. 5,286,800 and U.S. Pat. No. 5,401,805, techniques of obtaining polar group-containing olefin copolymers by adding alkyl borane such as 9-BBN to the terminal of the main or side chain of polyolefin and then radically polymerizing in the presence of oxygen the resulting polymer with methyl methacrylate (MMA) etc. However, the alkyl borane used in such techniques is generally expensive and unsuitable for industrial production. Further, the report of T. C. Chung et al. describes polymerization examples under heterogeneous conditions only at a MMA polymerization temperature of from room temperature to 60° C., but does not describe polymerization examples at high temperatures advantageous to higher reaction rate. It is noted that in the techniques of T. C. Chung et al., a radical polymerization-initiating terminal should be generated by using oxygen, and thus the radical polymerization reaction is inhibited due to the influence of residual oxygen, or proper active species are not formed due to oxidation into borate or boronate Macromolecules, 26, 3467 (1993), thus making it difficult to regulate the structure of the radically polymerized moiety.
The present invention was made to solve the above problems. That is, the object of the present invention is to provide a branched olefin copolymer particularly containing various polar functional groups in a branched region, which is excellent in adhesion to or compatibility with metal or polar resin, a process for efficiently producing the same, and uses thereof.